Recently, as part of efforts to address environmental issues, low-emission vehicles have been developed, and fuel cell vehicles having a fuel cell system as an in-vehicle power source are provided as one of the low-emission vehicles. The fuel cell system is an energy conversion system for supplying a reaction gas to a membrane electrode assembly in which an anode is disposed on one side of an electrolyte membrane and a cathode is disposed on the other side of the electrolyte membrane, and generating an electrochemical reaction, so as to convert chemical energy to electrical energy. Among the fuel cell systems, a solid polymer electrolyte fuel cell system in which a solid polymer membrane is used as an electrolyte is expected to be used as an in-vehicle power source since the solid polymer electrolyte fuel cell system can be miniaturized at low cost and has a high output density.
Water produced during the electrochemical reaction of the reaction gas, or humidifying water for the reaction gas remains in a gas channel of the fuel cell stack. When power generation is stopped with the remaining water left inside, the remaining water freezes in a low-temperature environment and diffusion of the reaction gas to the membrane electrode assembly is prevented. Thus, low-temperature startability is deteriorated.
Under such circumstances, a scavenging process of driving an air compressor by electric power from an electric storage device and draining water remaining in the gas channel of the fuel cell stack has been conventionally performed when power generation is stopped. Japanese Patent Laid-Open No. 2006-179472 discloses a method of determining whether the scavenging process is required when power generation is stopped and, when it is determined that the scavenging process is required, changing a charge threshold value for charging the electric storage device by the fuel cell stack to a higher value than a normal threshold value.
[Patent Document 1] Japanese Patent Laid-Open No. 2006-179472